Gas detectors often utilize infrared detection to detect the presence and concentration of certain gases in a particular area. When a gas is in the presence of infrared light, the gas can absorb some of the infrared light's energy. Specific gases absorb infrared light at specific wavelengths, allowing the identification of gases by measuring the absorption of light at those wavelengths. Optical filters are often used to pass only particular wavelengths for a gas of interest.
Gas detectors frequently incorporate high reflectance mirrors to reflect a light signal within a measuring chamber. A light source emits a light signal, such as infrared light, towards the high reflectance mirror. The high reflectance mirror then reflects the light signal towards a detector (such as an antenna). The detector compares the amount of light transmitted through the sample of gas. The detector can therefore determine the concentration of gas present in the sample by measuring the light that passes through the sample. For example, if the amount of light transmitted through the sample is equal to that of a reference gas, the sample may not contain a gas of interest. Conversely, a measured difference between the amount of light transmitted through the sample and the reference gas can quantitatively determine the concentration of gas in the sample.
A problem with conventional high reflectance mirrors is that they can suffer from significant reflection impairment at higher frequencies. This can be a problem, for example, at frequencies of several hundred gigahertz up into the terahertz range. This reflection impairment can obstruct a proper resonance of the mirror, negatively impacting operation of a gas detector.